My home is 55yrs old, on slab foundation, with copper pipes that I believe run through attic, and gas water heater. Have lived here 16yrs. and just now when using shower (with single handle Moen regulator installed by plumber 5 yrs ago) there is a loud "singing/whiring" noise that can be heard through wall. The sound begins after the water has been flowing through tub spout for a minute or so, changes pitch when tub diverter is flipped to showerhead, and also seems to change pitch depending on temperature position of valve. There is no banging as with hammer noises. Seems to be only the shower/tub lines that produce this noise. House is only 1000 sqft, so all plumbing (kitchen sink, washer, toilet, bathroom sink and shower) run through the same 10 ft. length of wall. Any ideas as to what causes this noise, is it an EMERGENCY that requires immediate (Saturday) attention, and is there anything else I should be concerned about? Thank You - I'll check back throughout the day - Michelle